Magnesium base alloys



June 18,1963 P. A; FISHER E-r'ALI 3,094,413

MAGNESIUM BASE ALLOYS Filed Sept. 14. 1960 PIC-3.2

P/f/A /P A. Ens 8 faw/ na A [MLEY United States Patent 3,094,413MAGNESIUM BASE ALLOYS Philip Andrew Fisher and Edward Frederick Emley,Manchester, England, assiguors to Magnesium Elektron Limited,Manchester, England Filed Sept. 14, 1960, Ser. No. 55,392 7 Claims. (Cl.75-435) This invention relates principally to the production ofmagnesium base alloys of the kinds which incorporate from 0.25% up toaluminium by weight of the alloy and more particularly from 0.25% to 2%aluminium. One object of the invention is to obtain a finer grain in thecast state than has hitherto been possible by any process with suchalloys when containing up to 2% aluminium. A further object of theinvention is to obtain magnesium aluminium alloys in the worked statewhich are particularly resistant to grain growth upon annealing. Stillanother object of the invention is to produce alloys containing bothzirconium and one or more of the incompatible elements such asaluminium, silicon, tin, manganese, cobalt, nickel, antimony, berylliumand iron which in molten magnesium will form a compound with zirconiumwhich tends to precipitate out of the melt. This phenomenon is describedin the specification of British Patent No. 511,137. Hereinafter we termthese elements zirconium-precipitating elements.

It is well known that magnesium alloys containing at least 2% aluminiumcan be treated with carbonaceous materials as described in Britishpatent specification No. 608,942, in order to produce a finer grain sizein the cast state. By this carbon grain refinement process it hashitherto been possible to obtain an average grain size of about 0.009mm. in a three inch thickness cast billet of an alloy containing 8%aluminium and the grain size of a similar billet in an alloy containing1% aluminium is about 0.6 mm.

Another method of refining the grain of such alloys is by thesuper-heating method which consists in heating the molten metal to atemperature above about 850 C. for a period of about 10-60 minutesbefore casting. This will produce approximately the same order of grainsize as the carbon inoculation treatment.

The addition of beryllium to such alloys has the advantageous effect ofreducing oxidation of metal in the molten state, but has the seriousdisadvantage that it prevents grain refinement by either carboninoculation or superheating. Moreover, beryllium itself coarsens thegrain size so that Mg-Al alloys containing beryllium are more coarsegrained than the same alloys when made without beryllium and given nograin refining treatment. The average grain size of a three inch thickcast billet of an alloy containing 0.8% aluminium and 0.005% berylliumis about 2 mm.

With a view to restoring the fine grain aiter adding beryllium it wasproposed in "British patent specification No. 511,291 to add zirconium.However, the real effect of this was to precipitate both zirconium andberyllium from the melt so that the final cast alloy contained little orno beryllium with consequent restoration of the grain size. The meltlikewise contained no zirconium. As correctly stated in British patentspecification No. 511,137, zirconium is precipitated from moltenmagnesium in the presence of aluminium and certain other elements but isnot so precipitated by other permissible elements such as zinc, cadmium,rare earth metals, silver, thallium, thorium, copper, bismuth, lead ancalcium.

We have now found it possible to incorporate both zirconium andaluminium in the same alloy in such a manner as to obtain a fine grainsize even with less than 2% aluminium present, and moreover to producewrought articles which are resistant to grain growth at elevatedtemperatures, so maintaining Well their tensile properties after hotforming, annealing, etc. We have also tound it possible to include otherzirconium precipitating elements instead of or in addition to aluminium.

According to the present invention the alloy contains from 0J1 to 0.7percent by weight zirconium and at least one of the followingzirconium-precipitating elements, viz:

Aluminium Over 0.1 and up to 10%.

Tin Over 0. 1 and up to 10%. Silicon Over 0.1 and up to 5%. Nickel Over0.1 and up to 2%. Cobalt Over 0.1 and up to 2%. Antimony Over 0.=l :andup to 2%.

Iron Over 0.01 and up to 0 .1%. Beryllium Over 0.005 and up to 0.03%.Manganese Over 0.5 and up to 2%.

with or without other elements as follows:

Zinc Up to 6.0 Thorium Up to 4.0 Cadmium Up to 6.0 Silver Up to 3.0 Rareearth metals Up to 8.0

One particularly useful range of alloys includes at least 0.25 percentaluminium and at least 0.2 percent zirconium.

The inclusion of aluminium has the advantage that a substantialproportion of it may remain out of combination with zirconium andtherefore be available for strengthening the alloy. The lower solubilityof iron in liquid magnesium will result in a smaller proportion ofzirconium compound being formed (although this may not be adisadvantage) while manganese and silicon both fall in a positionintermediate between aluminium and iron.

The alloys of the present invention are of course distinct from mixturesof similar composition formed by powder metallurgy and the alloys of thepresent invention are free from the stringers of oxide inclusionscharacteristic of articles made by powder metallurgy. The term alloys asused herein and in the appended claims is intended to exclude materialsmade by powder metallurgy.

The invention further comprises a method for obtaining such an alloywhich consists in flowing together two streams of molten magnesium basealloys one of which includes the zirconium-precipitating element orelements and the other of which includes the zirconium, casting thecombined stream and chilling it quickly whereby at least some of thesolid crystal nuclei derived from the molten zirconium alloy remainundissolved and so initiate crystallisation and at least some of theprecipitated zirconium-compound particles are retained in suspension inthe alloy. Preferably the quantity of suspended zirconium (i.e. thetotal zirconium content) is at least 0.2%. The soluble zirconium contentof the alloy if any is of course very small (e.g. 0.05%) because of thepresence of the zirconium precipitating element.

A particular method of carrying out the invention consists in flowingthe streams down separate ducts into a common launder whence it flows tothe tundish of a continuous or semi-continuous casting machine having abottomless mold. The two streams mix thoroughly in the launder andtundish and flow through into the mould which is open at the top andclosed at the bot-tom only by the solidified billet. Streams of coldwater are sprayed on to the billet as it is drawn continuously out ofthe bottom of the mould. Alternatively, a crucible divided into twoparts by a baflie plate may be used and the two metal streams flowedtogether at the crucible lip.

When this casting is subsequently extruded, forged or rolled, a wroughtproduct is produced which by virtue of the suspended zirconium-compoundparticles is very resistant to grain growth when the product issubjected to annealing or hot forming at elevated temperatures.

The invention has the further advantage of making it possible to includefor the first time substantial amounts of beryllium in a magnesium alloywith a fine grained cast structure. Thus it is possible to include from0.001% to 0.05% beryllium still retaining the required fine grain size.The beryllium will be incorporated in the stream which does not containthe zirconium, since beryllium has a very low solubility in the presenceof zirconium and is moreover a partial zirconium precipitator and istherefore included as a zirconium-precipitator for the purpose of thepresent invention.

The proportions of the two streams may be about equal or can be variedaccording to the required final composition.

The zirconium-bearing stream is preferably at a lower temperature thanthat at which zirconium was alloyed so as to ensure the presence ofcrystal nuclei in suspension.

For example, alloying may be carried out at 800 C. and pouring carriedout at 760 C.

By means of the present invention it is possible to obtain an averagegrain size of 0.1 mm. in a three inch thickness cast billet of an alloycontaining aluminium and 0.005% beryllium.

A specific application of the invention is to make Mg--3% All% Zn alloyrolling slab with fine grain size.

The quantities of elements other than aluminium and zirconium willnormally be within the following ranges:

The following are examples of compositions of the two streams and thefinal alloy produced.

( 1) Stream A: Percent Al 1.8 Be 0.03 Stream B:

Zr 0.6 Final alloy (50% A and 50% B): Al 0.9 Zr 0.3 Be 0.015 (2) StreamA:

A1 12 Zn 0.8 Mn 0.5 Stream B Zr 0.6 Final alloy (70% A and 30% B):

Al 8.4 Zn 0.56 Mn 0.35 Zr 0.18

(3) Stream A:

6.0 Mn 1.0 Stream B:

Zr 0.6 Final alloy (50% A and 50% B):

Th 3.0 Mn 0.5 Zr 0.3

4 (4) Stream A:

RE 1 Mn 1 Fe 0.04 Stream B:

Zr 0.6 Final alloy (50% A and 50% B):

RE 0.5 Mn 0.5 Fe 0.02

An apparatus suitable for the production of the alloys of the presentinvention is as shown in the accompanying diagrammatic drawings wherein:

FIGURE 1 is a side elevation of the apparatus; and

FIGURE 2 is a plan view thereof.

This apparatus comprises a crucible A divided into two compartments by:a partition B which extends from top to bottom of the crucible. Thecompartments have pouring lips C respectively adjacent one end of thetop of the partition. The partition is placed centrally to divide thecrucible into two equal halves each of which contains one of the twoalloys to be used. Providing that equal volumes of the two alloys areplaced in the crucible, when tilted this will deliver equal quantitiesof the two alloys simultaneously.

The partition may, however, be placed in a non-central position and soarranged that, on tilting, the desired proportions of the two alloys tobe mixed will be automatically delivered.

The alloys may be poured into an inclined trough D divided into twocompartments or channels by the partition E which extends to theposition F. The alloys are poured in separate streams until they meet ina tundish G where they mix and emerge through a funnel H. The mould intowhich they are to be cast will normally be placed immediately beneaththis funnel.

The apparatus may be of metallic construction, e.g. of steel, or of anyother material suitable for holding molten magnesium alloy.

The alloys may, however, also be prepared in, and poured from,completely separate crucibles providing that these are so arranged as todeliver the required proportions of each alloy simultaneously.

The launder D may also be dispensed with, the alloys being poureddirectly into a mixing compartment such as the tundish G.

The alloys may also be prepared in completely separate crucibles andseparately pumped to the mixing chamber, delivery of the requiredproportions of each alloy being arranged by suitable control of thepumping device.

We claim:

1. A magnesium base alloy containing from 0.1 to 0.7 percent by weightzirconium and at least one of the following zirconium-precipitatingelements, viz:

Aluminium Over 0.1 and up to 10%. Tin Over 0.1 and up to 10% SiliconOver 0.1 and up to 5% Nickel Over 0.1 and up to 2%. Cobalt Over 0.1 andup to 2% Antimony Over 0.1 and up to 2%.

Iron Over 0.01 and up to 0.1% Beryllium Over 0.005 and up to 0.03%.Manganese Over 0.5 and up to 2%.

characterized by a matrix of magnesium alloy containing a dispersion ofinsoluble intermetallic compounds consisting of zirconium with one ormore zirconium precipitating elements, the matrix being substantiallyfree from oxide, the quantity of suspended zirconium being at least 0.2percent while the dissolved zirconium is less than 0.05 percent.

Zinc Up to 6.0 Thorium Up to 4.0 Cadmium Up to 6.0 Silver Up to 3.0 Rareearth metals Up to 8.0

5. A process for the production of magnesium alloys containing bothzirconium and at least one element capable of precipitating zirconiumfrom a magnesium alloy which comprises the separate production of amolten magnesium zirconium alloy and a molten magnesium alloy containingat least one such element and flowing said alloys in separate streamsinto admixture with each other and thereupon rapidly solidifying themixture in a mold to retain the precipitate in solution.

6. A process for the production of magnesium alloys containing bothzirconium and at least one element capable of precipitating zirconiumfrom a magnesium alloy which comprises the separate production of amolten magnesium zirconium alloy and a molten magnesium alloy containingat least one such element and flowing the tWo alloys down separate ductsinto a common launder whence the mixed alloy flows to the mold. of abottomless mold casting machine and then rapidly solidifying the mixturein said mold to retain the precipitate in solution.

7. A process for the production of magnesium alloys containing bothzirconium and at least one element capable of precipitating zirconiumfrom molten magnesium alloy which comprises the separate production of amolten magnesium zirconium alloy and a molten magnesium alloy containingat least one such element and flowing said alloys in separate streamsinto admixture with each other and thereupon rapidly solidifying themixture in a mold to retain the precipitate in solution, the castingtemperature of the molten magnesium zirconium alloy being below that atwhich the Zirconium was alloyed to the magnesium.

References Cited in the file of this patent UNITED STATES PATENTS2,157,979 Cooper et a1 May 19, 1939 2,224,151 Gauthier Dec. 10, 19402,228,781 Breslau Jan. 14, 1941 2,656,269 Dunn et al Oct. 20, 19532,793,021 Courtney May 21, 1957 2,801,839 Lemmer Aug. 6, 1957 2,919,190Whitehead et al. Dec. 29, 1959 2,979,398 Foerster Apr. 11, 1961 FOREIGNPATENTS 806,103 Great Britain Dec. 17, 1958

1. A MAGNESIUM BASE ALLOY CONTAINING FROM 0.1 TO 0.7 PERCENT BY WEIGHTZIRCONIUM AND AT LEAST ONE OF THE FOLLOWING ZIRCONIUM-PRECIPITATINGELEMENTS, VIZ:
 2. AN ALLOY AS CLAIMED IN CLAIM 1 CONTAINING AT LEAST0.25 PERCENT ALUMINUM.